Replacement of the Power Button of your iPhone XS
Power buttons are a subtle reflection of trends in modern technology. When smartphones first came about, nearly every phone had a power button on top of the device. As screen sizes grew, and that top edge got farther and farther away from the reasonable reach of most thumbs, the power button migrated to the side. When screens grew larger and home buttons went extinct, the power button got built-in fingerprint sensors. And Apple is no different: the iPhone power button experiences the same trends.
So when Apple killed the home button, it changed two things about the power button, too. First, the power button on the iPhone X is twice as big as prior models, so it’s always easy to press it. And it now activates Siri when held down, instead of offering the shutdown prompt (the other main function of the iPhone home button). Both of these shifts make sense, logically. iPhones were getting bigger, and making the button easier to press is a natural extension of that. And as the last major button left on the phone, having the power button trigger Siri was essentially the only option (short of adding some kind of dedicated Siri button, anyway).
But the side effect is that the power button on current iPhones can’t actually do the one thing it’s supposed to: actually turn the phone on and off (a separate command that requires holding it and the volume up button together is needed to actually shut the phone off entirely).